He may have a serious brain or nerve problem, resulting from trauma, infection, calcium deficit, or even seizure or stroke. He needs to get to an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check the link http://www.aav.org/association/index.php?content=activeMembersList
for members of AAV in your area or call your regular vet and see who they recommend.
Do not let him have extra activity, as he may injure himself or become exhausted and frightened. Move the bird to an aquarium, box or carrier with soft towels in the bottom, no perch, and food and water in low bowls that he can reach easily. Put the whole thing on a heating pad on low or medium. Keep him partially covered, warm and quiet.
Pet/feed store medications are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them.
It is really important that the cause of the problem be discovered; he may need injectable calcium, antibiotics, fluids, oxygen therapy and many other medications. Act quickly and good luck.
Here are some other things to keep in mind before, during and after diagnosis/treatment:
Birds should be on a high-quality, preferably prescription, pelleted diet. In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.
Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.